Diesel engines can use particulate filters (DPFs) to reduce soot emissions. These filters trap particulate matter that is contained in the exhaust gasses passing through the filter. Periodically, when the filters become full of soot, they are regenerated by raising exhaust gas temperature to the point where the soot is burned. In this way, the filter is again able to retain soot and overall soot emissions are reduced.
DPF regeneration can be controlled based on differential pressure measured across the filter. As more and more soot is stored, a larger differential pressure is measured. See, for example, U.S. published application Ser. No. 2002/0,136,936. Also, degradation in the particulate filter can be determined from such a differential pressure sensor.
The inventors of the present invention have recognized a disadvantage with such systems. Specifically, if the pressure sensor is used to control regeneration is degraded, this can result in either too frequent, or too infrequent, DPF regeneration. Too frequent regeneration (from an erroneously high reading) can result in decreased fuel economy as energy is needlessly spent raising exhaust gas temperatures. Likewise, too infrequent regeneration (from an erroneously low reading) can result in impaired driveability. Further, a degraded sensor output can result in erroneous determinations that the DPF itself has become degraded, thereby resulting in replacement filter costs when no filter replacement may be required.